Tars are produced by the pyrogenesis of vegetable materials such as lignite, peat or wood in an air-free environment.
Coal is the main source, in which case the correct term to apply is "coal tar".
This is manufactured in either:
Coking plants, where coal is processed to manufacture the coke needed for the steel industry.
Gas plants, where coal is processed to manufacture lighting gas.
Use of tar for road building was halted more than ten years ago because of the health risk it posed for workers.
French and European toxicological studies have shown that the more Polycyclic Aromatic Hydrocarbons (PAH) a product contains the greater the health risk for those in contact with it.
In the case of coal tar (frequently referred to simply as tar) the fumes containing the PAHs are given off on heating to high temperatures.
In view of coal tar’s high PAH content, the Union des Syndicats de l‘Industrie Routière Française (USIRF) has recommended that it should no longer be used to manufacture hot mixes.
Applying the precautionary principle, the USIRF published this recommendation on 2 April 2002.